Hybrid optical recording discs are discs having a read-only memory (ROM) area containing pre-authored digital content and a recordable area for writing additional data which are recorded on the disc by a recorder or writer controlled by a computer. Such a disc has a substrate which can be formed by injection molding against a master plate so that the mastered substrate will have a continuous spiral track extending from a specified inner radius to a specified outer radius of the substrate. The spiral track is usually a groove which provides data channels on the disc and also provides for tracking of the disc while reading or recording data. The groove is wobbled with a characteristic frequency in a direction normal to the groove and is, therefore, referred to as a wobbled groove or a wobble groove. In the ROM area of a hybrid optical disc the groove is further modulated in the form of depressions which correspond to disc addressing data and to disc program data. The mastered substrate is then coated with a recording layer which can include an organic dye selected to absorb radiation in the recordable wavelength of the writer. Upon coating the recording layer with a metal layer, a reflective layer is formed over the entire recording layer. A protective layer, usually of a polymer organic material, is formed over the reflective layer.
Hybrid optical discs follow the specifications of the Orange Book and the Red Book, published by Philips Electronics N.V. and Sony Corporation. The Orange Book specifies that the logical structure of hybrid discs largely follow the specifications for Read-Only-Memory CD's (CD-ROM) and Write-Once CD's (CD-WO). In particular, the smallest division that a disc can have and be considered complete (or “fixated”) is known as a “session”. In its most basic form, a session includes three major segments. A session includes a preliminary area, called the “lead-in”, which identifies the start of a session and includes certain specified information about the session, such as the table of contents. The lead-in area is followed by the data, which consists of a series of blocks of digital data encoded in eight-to-fourteen modulation (EFM). The data can be from numerous sources in numerous digital formats, including audio, executable applications, video, photographic images, numerical data, etc. The session is completed by a “lead-out” section, which signals the end of the session, and also points to the next session, if it exists.
A hybrid optical disc generally consists of one or more sessions of preformed data that are mastered onto the disc by any well-known mastering techniques. The mastering process also formats the remainder of the disc as a write-once recordable area. The master produced this way is then used in any well-known molding or stamping technique to mass-produce hybrid optical discs with a pre-recorded area, containing one or more sessions, and a recordable area. A user may then record information in the recordable area in a secondary writing operation using a writing device (such as a CD-R or CD-RW drive), usually attached to a computer system.
The sessions that were mastered on the discs were fixated, and cannot be added to, so the newly recorded information is recorded to a new session. While certain writing techniques (called Track-at-once recording and packet recording) allow less than a complete session to be written at once, the session is not considered complete until both the lead-in and lead-out are written. This process is called fixating in the art. Once a session is fixated, it is defined as complete by Orange Book standards and no further data may be written to it.
Sometimes, it is desired to write a small amount of unique user data to each disc. An example of this would be writing a unique serial number to each to differentiate that disc from all others in subsequent use. Another example would be a user's name and address. The Orange Book specifies that a session must have at least 300 blocks (of 2048 bytes each) of information, which is about 614 Kbytes. As also defined by the Orange Book, each session must also have lead-in and lead-out areas, which require an additional 13.8 megabytes of data that must be written for each session. Current systems require that this lead-in and lead-out data be written at the same time as, or after, the unique user data is written. Thus, conventional systems need to write 14.4 megabytes of data to the disc, even if the unique data of interest is only a very small fraction of this.
Since 614 kilobytes corresponds to 100 to 200 pages of typed text, it will be clear that there are many cases (in addition to serial numbering mentioned above) in which only a small amount of user data needs to be written to a disc. In these cases, the disc writer spends a disproportionate amount of time writing the 13.8 megabytes of session structural data in comparison to the amount of data being written.